The activation of proto-oncogenes and the inactivation of tumor suppressors drive tumor formation in vivo and the transformation of cells in culture. However, other genes that contribute to the transduction of oncogenic signals can modify tumor susceptibility. Kinase Suppressor of Ras 1 (KSR1) is a modifier of tumorigenesis and cell transformation by oncogenic Ras. The goal of this research is to explain the molecular mechanisms underlying the action of KSR1. Recent data from this laboratory demonstrate that KSR1 has properties expected of a molecular scaffold for the Raf/MEK/ERK signaling cassette. Furthermore, deletion of KSR1 prevents constitutively active RasV12 from transforming cells in culture and markedly diminishes RasV12-induced tumor formation in vivo. New data demonstrate that KSR1 interacts with caveolin-1 to regulate the subcellular assembly and activation of the Raf/MEK/ERK signaling cassette in a manner critical to RasV12-induced transformation and tumorigenesis. Experiments also demonstrate that the related protein, KSR2, has a distinct effect on cell proliferation and metabolism. A third set of studies reveal the interaction of KSR proteins with a kinase family that affects their function. These observations suggest a previously unidentified, but physiologically important, interdependence of mechanisms contributing to tumorigenesis via the Raf/MEK/ERK signaling cassette and mechanisms regulating cellular metabolism. This proposal will test the hypothesis that KSR proteins affect tumorigenic potential via mechanisms that are dependent and independent of the Raf/MEK/ERK kinase cascade. The details of those mechanisms will be revealed by: 1) determining the contribution of KSR1 in the spatial regulation of ERK activation and cell transformation, 2) determining the role of KSR2 in regulating KSR1 function and RasV12 tumorigenesis, and 3) determining the role of effectors of energy balance in regulating KSR proteins and activated RasV12. PUBLIC HEALTH RELEVANCE: The proto-oncogene Ras is a commonly mutated contributor to multiple human cancers. KSR1 plays a potent role in regulating the tumorigenic potential of Ras. Thus, study of KSR proteins in the regulation of tumor formation is likely to provide novel insights into the molecular mechanisms regulating cancer susceptibility.